Binder compositions for fiber containing products have a variety of uses that include stiffening applications where the binder is used to stiffen a fiber containing product; thermo-forming applications wherein the binder resin is applied to a sheet or lofty fibrous product, following which it is dried and optionally B-staged to form an intermediate and still curable product; and forming fully cured systems such as building insulation.
One important application of binder compositions is to form fibrous glass into insulation. Fiberglass insulation generally includes matted glass fibers bonded together by a cured thermoset polymeric material. Molten streams of glass are drawn into fibers of random lengths and blown into a forming chamber where they are randomly deposited as a mat onto a traveling conveyor. The glass fibers, while in transit in the forming chamber and still hot from the drawing operation, are sprayed with an aqueous binder composition. The residual heat from the glass fibers and the flow of air through the fibrous mat during the forming operation are generally sufficient to volatilize water from the binder, thereby leaving the remaining components of the binder on the fibers as a viscous or semi-viscous high solids liquid. The coated fibrous mat is transferred to a curing oven where heated air is blown through the mat to cure the binder and rigidly bond the glass fibers.
Conventional binder compositions for fiberglass include phenol-formaldehyde binders, which are favored for their low cost and the ability to go from a low viscosity liquid in the uncured state to a rigid thermoset polymer when cured. A low viscosity uncured binder allows the mats to be properly sized. In contrast, viscous binders are usually sticky and promote fiber accumulation on surfaces of the production equipment. Some of this accumulated fiber inevitably falls on the mat, causing dense areas and defects in the fiberglass. After the binder composition is applied and cured, however, it should be transformed from a low viscosity liquid to a rigid matrix. This allows the fiberglass insulation to spring from a compressed volume when packaged, back to its uncompressed full size when installed.
Numerous thermosetting polymers can go from low viscosity liquids to rigid polymer matrices when cured. However, binder-coated fiberglass is typically viewed as a commodity, and subject to intense cost pressures. The economics rule out the use of most thermosetting polymer resins, including many polyurethanes and epoxies, among other resins. The success of phenol-formaldehyde resins is due in part to their excellent cost/performance ratio. Phenol-formaldehyde resins can be economically produced, and can be extended with urea prior to use as a binder in many applications. Such urea-extended phenol-formaldehyde binders have been the mainstay of the fiberglass insulation industry for years.
More recently, concerns about emissions of volatile organic compound (VOCs) and other environmental contaminants have provided an impetus to reduce the use of formaldehyde-based binders. Fiberglass producers have experimented with changes in the ratio of phenol to formaldehyde in the phenol-formaldehyde resole resins, as well as changes in catalysts, and the addition of formaldehyde scavengers. While these changes have resulted in considerable improvement in emissions from the binders, increasingly stringent government regulations have encouraged producers to formulate binders that are essentially formaldehyde free.
One alternative binder formulation replaces the phenol-formaldehyde with polycarboxy polymers. While the polycarboxy binders are cost competitive with phenol-formaldehyde from a materials standpoint, they can be tough on manufacturing equipment. The polycarboxy binders are made under very acidic conditions, typically starting with aqueous solutions of acrylate and/or methacrylate monomers (e.g., acrylic acid and/or methacrylic acid) that have a pH of about 2 to 4. Production equipment that comes in contact with these solutions often requires repair and replacement at an accelerated pace due to the highly acidic environment. Thus, there is a need for binder compositions and method of making them that does not require such highly acidic conditions. These and other problems are addressed here.